Process for preparing vinyl phosphonic acid

ABSTRACT

Vinyl phosphonic acid is produced by the hydrolysis of a vinyl phosphonic acid ester (e.g. “Bis Beta”) in the presence of a carbonyl compound (e.g. a monofunctional or difunctional aldehyde or a ketone).

[0001] This invention relates to the production of vinyl phosphonic acidand in particular to the production of vinyl phosphonic acid byhydrolysis of a corresponding ester.

[0002] Vinyl phosphonic acid is a useful ingredient in the production offlame-retardant agents. Polymers of vinyl phosphonic acid can be used inpaints, plastics materials and corrosion inhibitors, amongst others.

[0003] It is known to produce vinyl phosphonic acid by hydrolysis of acorresponding ester in the presence of an acidic or a basic catalyst.However, the product of such a hydrolysis has been found to besubstantially impure and contaminated with alcohols and other organics.

[0004] We have discovered that hydrolysis of an ester (especially ahalogenated ester) of vinyl phosphonic acid in the presence of acarbonyl compound (e.g. an aldehyde or a ketone) leads to the productionof substantially pure vinyl phosphonic acid in good yield.

[0005] Although the present invention will be described herein withparticular reference to the production of vinyl phosphonic acid by thehydrolysis of a bis (beta haloalkyl) ester of the acid, it is not to beconstrued as being limited thereto.

[0006] Accordingly, the present invention provides a method for theproduction of vinyl phosphonic acid, in which a vinyl phosphonic acidester is hydrolysed in the presence of a carbonyl compound.

[0007] The present invention also provides vinyl phosphonic acid made bythe method described in the immediately preceding paragraph.

[0008] In one embodiment of the present invention, the carbonyl compoundmay be a monofunctional aldehyde of general formula:

(R—CHO)_(n)

[0009] wherein R represents hydrogen or an alkyl group having from 1 to10 carbon atoms and n is a whole number of 1 or greater.

[0010] The aldehyde may be, for example, formaldehyde, paraformaldehyde,metaformaldehyde or acetaldehyde.

[0011] In a second embodiment of the present invention, the carbonylcompound may be a difunctional aldehyde of general formula:

[0012] wherein n is zero or a whole number of from 1 to 4.

[0013] An example of such a difunctional aldehyde is glyoxal.

[0014] In a third embodiment of the present invention, the carbonylcompound may be a ketone of general formula:

[0015] wherein R¹ and R² (which may be the same or different) eachrepresent an alkyl group having from 1 to 5 carbon atoms.

[0016] The ketone may, for example, be acetone.

[0017] Alternatively, the carbonyl compound may be a cycloalkyl ketone,for example, cyclohexanone.

[0018] Suitably, the ester which is to be hydrolysed is abis(beta-haloalkyl) ester of vinyl phosphonic acid, preferably thebis(beta-chloroethyl) ester (hereinafter “BisBeta”).

[0019] According to the present invention, the carbonyl compound ispresent in an amount of from 1 to 250 mole %, suitably from 50 to 200mole % (with respect to the ester).

[0020] The hydrolysis is preferably carried out at a temperature ofabout 140°-150° C. and for a time of 30 to 40 hours.

[0021] The hydrolysis may be carried out at atmospheric pressure.Alternatively, the hydrolysis may be carried out at a pressure of up to10 atmospheres (preferably from 1 to 4 atmospheres).

[0022] Suitably, the hydrolysis may be carried out under an inert (e.g.nitrogen) atmosphere.

[0023] The hydrolysis may conveniently be carried out in the presence ofan initial acid catalyst (e.g. sulphuric acid or a heel of vinylphosphonic acid) in an amount of from 1 to 10 mole % (with respect tothe ester).

[0024] The present invention will be illustrated by way of the followingexamples:

[0025] In the examples, “Bisbeta” signifies the bis(beta-chloroethyl)ester of vinyl phosphonic acid and “VPA” signifies vinyl phosphonic aciditself.

EXAMPLE 1

[0026] A 5 litre flask fitted with stirrer, nitrogen inlet, condenser,thermometer, and addition tube (from peristaltic pump) was charged withBisBeta (5000 g, 21.45 mol) and VPA (231 g, 2.14 mol) and heated to 150°C. A 5% w/w solution of formaldehyde in water was then slowly fed in viathe addition tube at a rate of approx 5 cm³/min for 30-40 h. Distilledwater was then fed in at the same rate for a further 6 h to removeresidual formaldehyde and other volatiles. The final reaction mixturewas then cooled to 100° C. and dried under reduced pressure to give VPA(92% by ³¹P nmr).

EXAMPLE 2 (Comparative Example)

[0027] A 1 litre flask fitted with stirrer, nitrogen inlet, condenser,thermometer, and addition tube (from peristaltic pump) was charged withBisBeta (500 g, 2.14 mol) and VPA (34.8 g, 0.32 mol) and heated to 150°C. Water was then slowly fed in via the addition tube at a rate ofapprox. 5 cm³/min for 30 to 40 h.

[0028] The final reaction mixture was then cooled to 100° C. and driedunder reduced pressure to give VPA (78% by ³¹P nmr). The main impuritiesfound in the VPA comprised ethylene glycol (shown to be present by ¹³Cnmr).

EXAMPLE 3

[0029] A 1 litre flask fitted with stirrer, nitrogen inlet, condenser,thermometer, and addition tube (from peristaltic pump) was charged withBisBeta (500 g, 2.14 mol) and VPA (34.8 g, 0.32 mol) and heated to 150°C. Water was then slowly fed in via the addition tube at a rate ofapprox. 5 cm³/min for 30-40 h. Paraformaldehyde (10 g, 0.33 mol) wasthen added as a solid and water was added at the same rate as above fora further 4 h. The reaction mixture was shown to be 87% VPA by ³¹P nmr.

[0030] It will be seen that VPA of improved purity was obtained whenExample 3 was carried out on the final mixture of Example 2.

EXAMPLE 4

[0031] A 2 litre flask fitted with stirrer, nitrogen inlet, condenser,thermometer and addition tube (from peristaltic pump) was charged withBisBeta (2000 g, 8.58 mol) and VPA (92.7 g, 0.86 mol) and heated to 150°C. A 15% wt/wt solution of formaldehyde in water was slowly fed via theaddition tube at a rate of 0.4 cm³/min for 33 h. Distilled water wasthen fed in at 1.2 cm³/min for 7 h to remove residual formaldehyde. Thefinal reaction mixture was then cooled to 100° C. and dried underreduced pressure to give VPA (90% by ³¹P nmr).

EXAMPLE 5 (Pilot Plant Scale)

[0032] BisBeta (1600 kg, 6.86 kmol) and VPA (40 kg, 0.37 kmol) werecharged to a 300 gallon reactor, set to condense and distil into aseparate receiver. The system was pressurised to 1 bar (g) with nitrogenand maintained at that pressure. The mixture was heated to 140° C. andstirred. Steam (added through a sparge pipe at a rate of 50-70 kg/hr)and formaldehyde (1328 kg, 30% wt/wt; 13.28 kmol) were added, both overa period of 36 hours. The mixture was cooled and water/organicsdistilled off under reduced pressure to a final distillation temperatureof 100° C.

[0033] On cooling a product of >90% mol purity was obtained.

1. A method for the production of vinyl phosphonic acid comprisinghydrolysing phosphonic acid ester in the presence of a carbonylcompound.
 2. A method according to claim 1, in which the carbonylcompound is a monofunctional aldehyde of general formula (R—CHO)_(n)wherein R represents hydrogen or an alkyl group having from 1 to carbonatoms and n is a whole number of 1 or greater.
 3. A method according toclaim 2, in which the aldehyde is formaldehyde, paraformaldehyde ormetaformaldehyde.
 4. A method according to claim 2, in which thealdehyde is acetaldehyde.
 5. A method according to claim 1, in which thecarbonyl compound is a difunctional aldehyde of general formula

wherein n is zero or a whole number of from 1 to
 4. 6. A methodaccording to claim 5, in which the aldehyde is glyoxal.
 7. A methodaccording to claim 1, in which the carbonyl compound is a ketone ofgeneral formula:

wherein R¹ and R² (which may be the same or different) each represent analkyl group having from 1 to 5 carbon atoms.
 8. A method according toclaim 7, in which the ketone is acetone.
 9. A method according to claim1, in which the carbonyl compound is a cycloalkyl ketone.
 10. A methodaccording to claim 9, in which the ketone is cyclohexanone.
 11. A methodaccording to claim 1, in which the ester is a bis(beta-haloalkyl) esterof vinyl phosphonic acid.
 12. A method according to claim 11, in whichthe ester is the bis(betachloroethyl) ester of vinyl phosphonic acid.13. A method according to claim 1, in which the carbonyl compound ispresent in an amount of from 1 to 250 mole % (with respect to theester).
 14. A method according to claim 13, in which the carbonylcompound is present in an amount of from 50 to 200 mole % (with respectto the ester).
 15. A method according to claim 1, in which thehydrolysis is carried out at a temperature of about 140-150° C. and fora time of 30 to 40 hours.
 16. A method according to claim 1, in whichthe hydrolysis is carried out at a pressure of from 1 to 10 atmospheres.17. A method according to claim 16, in which the hydrolysis is carriedout at a pressure of from 1 to 4 atmospheres.
 18. A method according toclaim 1, in which the hydrolysis is carried out under an inertatmosphere.
 19. A method according to claim 18, in which the hydrolysisis carried out under nitrogen.
 20. A method according to claim 1, inwhich the hydrolysis is carried out in the presence of an initial acidcatalyst.
 21. A method according to claim 20, in which the initial acidcatalyst is sulphuric acid and is present in an amount of from 1 to 10mole % (with respect to the ester).
 22. A method according to claim 20,in which the initial acid catalyst comprises a heel of vinyl phosphonicacid.